Fluid pressure operated press-riveting device

ABSTRACT

The present application pertains to a fluid pressure operated press-riveting device, comprising: a cylinder having a distal end, a proximal end and a sidewall extending axially between the distal end and the proximal end, wherein the distal end has an opening section; a first piston in the cylinder, which defines a first inner chamber with the proximal end and has a press-riveting rod extending towards the distal end and aligned with the opening section; a second piston in the cylinder, which defines a second inner chamber with the distal end, and has a sleeve section extending to the distal end, which at least extends to and closes the opening section and can accommodate the press-riveting rod; a fluid pump system, which is respectively connected with the first inner chamber and the second inner chamber to supply fluid thereto or suck fluid back therefrom, so that the first piston and the second piston move axially along the cylinder, when the second piston moves to the distal end, the sleeve section moves to a pre-compression position, and then the press-riveting rod protrudes out for press-riveting; a force transmission member disposed between the first piston and the second piston, wherein when the sleeve section reaches the pre-compression position, the first piston can approach the second piston, and apply a pressing force to the second piston through the force transmission member.

TECHNICAL FIELD

The present invention pertains to riveting technology, more specifically, to a fluid pressure operated press-riveting device.

BACKGROUND ART

Press-riveting is a riveting method using the static pressure generated by the press-riveting machine to upset the rivet to form a header. The press-riveted parts have the characteristics of good surface quality, small deformation, and high connection strength, so they are widely used in various machining fields, such as shipbuilding, automobile manufacturing, aerospace, white goods, etc. However, in some machining environments, the internal space of the part to be machined is limited, and traditional press-riveting devices typically have long axial lengths, making them unsuitable for operation in such small workspaces.

SUMMARY OF INVENTION

The present application provides a press-riveting device with a short axial length, which can be suitable for operation in small workspaces.

In one aspect of the present application, a fluid pressure operated press-riveting device is provided, comprising: a cylinder having a distal end and a proximal end disposed opposite to each other, and a sidewall extending axially between the distal end and the proximal end, wherein the distal end has an opening section; a first piston, wherein the first piston is disposed in the cylinder and defines a first inner chamber together with the proximal end, and wherein the first piston has a press-riveting rod extending towards the distal end and aligned with the opening section; a second piston, wherein the second piston is disposed in the cylinder and defines a second inner chamber together with the distal end, the second piston has a sleeve section extending towards the distal end, the sleeve section extends at least to the opening section to close the opening section, and the sleeve section slidably accommodates the press-riveting rod; a fluid pump system, wherein the fluid pump system is in fluid communication with the first inner chamber and the second inner chamber, respectively, and is used to supply fluid to or suck fluid back from the first inner chamber and the second inner chamber, so that the first piston and the second piston can reciprocate axially along the cylinder, and wherein when the first piston and the second piston move from the proximal end to the distal end, the sleeve section moves to a pre-compression position, and then the press-riveting rod protrudes out of the sleeve section to perform a press-riveting operation on a workpiece to be press-riveted; and a force transmission member disposed between the first piston and the second piston, wherein when the sleeve section of the second piston reaches the pre-compression position, the first piston can approach the second piston and apply a pressing force to the second piston through the force transmission member.

In some embodiments, the force transmission member comprises a spring element, with its two ends are connected with the first piston and the second piston, respectively.

In some embodiments, the spring element is a Belleville spring element.

In some embodiments, the force transmission member comprises a third inner chamber defined jointly by the first piston, the second piston and the sidewall of the cylinder, and the fluid pump system is also in fluid communication with the third inner chamber to supply fluid to or suck fluid back from the third inner chamber.

In some embodiments, a pressure regulating valve is disposed between the third inner chamber and the fluid pump system to adjust a fluid pressure in the third inner chamber.

In some embodiments, a press-riveting end is disposed at an end of the press-riveting rod.

In some embodiments, the press-riveting end is detachably connected with the press-riveting rod.

In some embodiments, the sleeve section comprises a stop element to limit a length of the press-riveting end protruding from the sleeve section.

In some embodiments, a seal is disposed at a contact portion of the first piston or the second piston with a surface of the cylinder.

In some embodiments, the press-riveting device further comprises a displacement sensor connected with the first piston and is configured to indicate an axial position of the first piston.

In some embodiments, the fluid pump system comprises a fluid pump, and the first inner chamber and the second inner chamber are in fluid communication with each other through the fluid pump.

In some embodiments, the fluid supplied and sucked by the fluid pump system is hydraulic oil.

The above is an overview of the present application, and may be simplified, may be summarized, and may omit the details. Therefore, those skilled in the art shall understand that this part is only illustrative and is not intended to limit the protection scope of the present application in any way. This summary is neither intended to determine the primary features or essential features of the subject matter sought to be protected, nor intended to be used as an auxiliary means to determine the protection scope of the subject matter sought to be protected.

BRIEF DESCRIPTION OF DRAWINGS

The above and other features of the disclosure of the present application will be more fully and clearly understood through the following description and appended claims in combination with the drawings. It can be understood that these figures only illustrate several embodiments of the disclosure of the present application, and therefore should not be considered as limiting the protection scope of the scope of the present application. By adopting the drawings, the content of the present application will be explained more clearly and in detail.

FIGS. 1 to 3 show a schematic diagram of a press-riveting device 100 according to an embodiment of the present application; among them, FIG. 1 is a schematic diagram of the appearance of the press-riveting device 100; FIG. 2 is a side view of the press-riveting device 100; FIG. 3 is a cross-sectional view of the press-riveting device 100 along the AA direction shown in FIG. 2, wherein the press-riveting device 100 is in an initial state;

FIGS. 4 to 6 show a schematic diagram of a press-riveting device 200 according to an embodiment of the present application; among them, FIG. 4 is a schematic diagram of the appearance of the press-riveting device 200; FIG. 5 is a side view of the press-riveting device 200; FIG. 6 is a cross-sectional view of the press-riveting device 200 along the AA direction shown in FIG. 5, wherein the press-riveting device 200 is in an initial state;

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, refer to the drawings constituting a part thereof In the drawings, similar reference numerals usually represent similar components unless the context indicates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not intended to limit. Without departing from the spirit or protection scope of the subject matter of the present application, other embodiments may be adopted, and other changes may be made. It can be understood that various aspects of the content of the present application generally described in the present application and illustrated in the drawings can be configured, substituted, combined, and designed with various configurations, and all of these clearly constitute a part of the content of the present application.

FIGS. 1 to 3 show a schematic diagram of a press-riveting device 100 according to an embodiment of the present application; among them, FIG. 1 is a schematic diagram of the appearance of the press-riveting device 100; FIG. 2 is a side view of the press-riveting device 100; FIG. 3 is a cross-sectional view of the press-riveting device 100 along the AA direction shown in FIG. 2, wherein the press-riveting device 100 is in an initial state. In some embodiments, the press-riveting device 100 is designed to be an automated or semi-automated device, powered by an external power source or a built-in power source, and used for press-riveting processing of the workpiece to be processed.

Specifically, as shown in FIGS. 1 to 3, the press-riveting device 100 comprises a cylinder 101, and a first piston 102 and a second piston 103 disposed in the cylinder 101. Among them, the cylinder 101 is generally cylindrical, and the first piston 102 and the second piston 103 can move axially along the cylinder 101. The cylinder 101 is mainly constructed of a proximal end cylinder cover 111 and a distal end cylinder cover 112 and a sidewall 113 extending between the two cylinder covers, wherein an opening section 114 is provided on the distal side cylinder cover 112. In some embodiments, the sidewall 113 is connected with the cylinder cover 111 and/or 112 at two ends by means of connections such as welding, gluing, etc. In some embodiments, the sidewall 113 is connected with the cylinder cover 111 and/or 112 at two ends through a detachable connection such as a threaded connection and a snap connection. In some embodiments, the sidewall 113 is integrally formed with at least one of the cylinder covers 111 and 112. In some embodiments, the shape of the opening section 114 on the distal end cylinder cover 112 is circular, while in other embodiments, the opening section 114 may also be in other shapes such as triangle, ellipse, or square. It should be noted that the distal or the distal end described herein refers to the end or side of the press-riveting device adjacent to the workpiece to be press-riveted when used, and the proximal or the proximal end refers to the opposite end or side.

Continue to refer to FIG. 3, wherein the first piston 102, the proximal end cylinder cover 111 of the cylinder 101 and part of the sidewall 113 jointly define a closed first inner chamber 121. As shown in the figure, the first piston 102 further has a press-riveting rod 122 extending to the distal end, and the press-riveting rod 122 can be aligned with the opening section 114 and pass through the opening section 114. In some embodiments, the press-riveting rod 122 is connected with the first piston 102 by means of any applicable connection, such as welding, gluing, a threaded connection, and a snap connection. In some embodiments, the press-riveting rod 122 and the first piston 102 are integrally formed. As shown in FIG. 3, a press-riveting end 123 is disposed at an end of the press-riveting rod 122, and the press-riveting end 123 accompanies the first piston 102 and the press-riveting rod 122 in an axial movement along the cylinder 101, thereby directly acting on the workpiece to be press-riveted and completing the press-riveting operation. In some embodiments, the press-riveting end 123 is connected with the press-riveting rod 122 by means of connections such as welding, gluing, etc., or is integrally formed with the press-riveting rod 122. In some embodiments, the press-riveting end 123 is detachably connected with the press-riveting rod 122 through a threaded connection, a snap connection, etc., so that the operator can replace it with other suitable press-riveting ends as needed, thereby expanding the applicability of the press-riveting device 100.

As shown in FIG. 3, the second piston 103 has a sleeve section 132 extending to the distal end, and the sleeve section 132 extends to contact the opening section 114, so that the second piston 103, together with the sleeve section 132, and the distal end cylinder cover 112 and part of the sidewall 113 of the cylinder 101 jointly define a closed second inner chamber 131. As mentioned above, in some embodiments, the opening section 114 may be in the shape of circle, triangle, ellipse, square or other shapes. Therefore, in order to define the closed second inner chamber 131, the sleeve section 132 may also be in the shape of circle, triangle, ellipse, square or other shapes to match the opening section 114. Although the sleeve section 132 and the second piston 103 shown in the figure are integrally formed, in some embodiments, the sleeve section 132 can also connect with the second piston 103 by means of any applicable connection, such as welding, gluing, a threaded connection and a snap connection. As shown in the figure, the press-riveting rod 122 of the first piston 102 is accommodated in the sleeve section 132 and can slide axially along the sleeve section 132.

The volume of the first inner chamber 121 can be changed with the movement of the first piston 102 along the axial direction of the cylinder 101. Similarly, the volume of the second inner chamber 131 can be changed with the movement of the second piston 103 along the axial direction of the cylinder 101. Specifically, the press-riveting device 100 in FIG. 3 is in its initial state, that is, the state when the press-riveting operation has not been started or a single press-riveting operation has already been completed. In this initial state, the first piston 102 and the second piston 103 are relatively close to the proximal end cylinder cover 111, so that the volume of the first inner chamber 121 is in a relatively small state and the volume of the second inner chamber 131 is in a relatively large state. When the press-riveting device 100 starts to perform the press-riveting operation, with the movement of the first piston 102 and the second piston 103 toward the distal end, the volume of the first inner chamber 121 gradually increases while the volume of the second inner chamber 131 gradually decreases.

As shown in FIG. 3, a spring element 104 is disposed between the first piston 102 and the second piston 103. Two ends of the spring element 104 are respectively connected with the first piston 102 and the second piston 103. In some embodiments, the spring element 104 is a Belleville spring element. In some embodiments, the spring element 104 is in any other viable form of spring, such as a coil spring, an air spring, etc. Due to the presence of the spring element 104, when the sleeve section 132 of the second piston 103 moves to abut the workpiece to be press-riveted, the second piston 103 stops moving, and the first piston 102 continues to move along the axial the cylinder 101 toward the second piston and gradually compresses the spring element 104, thereby applying pressure on the second piston 103 through the spring element 104, so that the sleeve portion 132 can further compress the workpiece to be press-riveted. It can be understood that the magnitude of the pressing force of the sleeve section 132 applied on the workpiece to be press-riveted depends primarily on the elasticity of the spring element 104.

The press-riveting device 100 also has a fluid pump system 105 (not shown in the figures). The fluid pump system 105 comprises a fluid pump, a driving motor, and a fluid storage device, the fluid pump system 105 and the first inner chamber 121 communicate through a first through hole 124 shown in FIG. 1, and the fluid pump system 105 and the second inner chamber 131 communicate through a second through hole 133 as shown in FIG. 1. In some embodiments, the first through hole 124 and the second through hole 133 are respectively disposed on the proximal end cylinder cover 111 and the distal end cylinder cover 112. In some embodiments, the first through hole 124 and the second through hole 133 may also be disposed on the sidewall 113 of the cylinder 101. Driven by the driving motor, the fluid pump inputs or outputs the fluid stored in the fluid storage device through the first through hole 124 and the second through hole 133 into or out of the first inner chamber 121 or the second inner chamber 131, causing the first piston 102 and the second piston 103 to move along the axial direction of the cylinder 101 under the effect of fluid pressure. For example, as the fluid pump inputs fluid into the first inner chamber 121, the pressure generated by the fluid in the chamber pushes the first piston 102 to move axially along the cylinder 101 toward the distal end. As the fluid pump inputs fluid into the second inner chamber 131, the pressure generated by the fluid in the chamber pushes the second piston 103 to move axially along the cylinder 101 toward the proximal end.

In some embodiments, the fluid pump system 105 described above may not have a fluid storage device. The first inner chamber 121 and the second inner chamber 131 are in direct fluid communication through the fluid pump. Driven by the driving motor, the fluid pump guides the fluid in the second inner chamber 131 into the first inner chamber 121. At this time, under the effect of fluid pressure in the chambers and the spring element 104, the first piston 102 and the second piston 103 both move along the axial direction of the cylinder 101 toward the distal end. In the opposite process, the fluid pump guides the fluid in the first inner chamber 121 into the second inner chamber 131. At this time, under the effect of fluid pressure in the chambers and the spring element 104, the first piston 102 and the second piston 103 both move along the axial direction of the cylinder 101 toward the proximal end. Such an arrangement enables the structure design of the press-riveting device 100 to be more compact and simpler. In some embodiments, the fluid pump system 105 described above is further provided with a valve to control the supply flow rate or the return flow rate of the first inner chamber 121 and the second inner chamber 131. It should be pointed out that the fluid described herein can be liquid or gas, preferably hydraulic oil.

The working process of this embodiment is specifically described below:

Referring to FIGS. 1 and 3, when a press-riveting process needs to be performed on the workpiece to be press-riveted, the press-riveting end 123 of the press-riveting device 100 is aligned with the position to be machined on the workpiece to be press-riveted. The driving motor of the fluid pump system 105 starts to operate, driving the fluid pump to input fluid into the first inner chamber 121 and to draw fluid from the second inner chamber 131, thereby causing the first piston 102 and the second piston 103 to move along the axial direction of the cylinder 101 toward the distal end. The press-riveting end 123 and the sleeve section 132 accompany the first piston 102 and the second piston 103 in the movement toward the distal end, and when the sleeve section 132 abuts the workpiece to be press-riveted, the sleeve section 132 reaches the pre-compression position. Subsequently, the second piston 103 stops moving and the first piston 102 continues to move along the axial direction of the cylinder 101 toward the distal end, and with the movement of the first piston 102, the press-riveting end 123 moves along the axis of the sleeve section 132 toward the distal end. Because the spring element 104 is connected between the first piston 102 and the second piston 103, as the first piston 102 approaches the second piston 103, the gradually compressed spring element 104 applies gradually increasing pressing force on the second piston 103, so that the workpiece to be press-riveted can be better fixed, ensuring the accuracy of the press-riveting position. Subsequently, the press-riveting rod 122 protrudes out of the sleeve section 132 to press-rivet the workpiece to be press-riveted, which is compressed by the sleeve section 132.

When the press-riveting is completed, the driving motor drives the fluid pump to suck fluid from the first inner chamber 121 and input fluid into the second inner chamber 131, so that the first piston 102 and the second piston 103 move one after another along the axial direction of the cylinder 101 toward the proximal end. After that, the first piston 102 and the second piston 103 gradually reset to the initial state shown in FIG. 3, and the press-riveting device 100 completes a single press-riveting operation.

As shown in FIG. 3, the sleeve section 132 is further provided with a stop element 134 to limit the length of the press-riveting end 123 protruding from the sleeve section. At the same time, the proximal end cylinder cover 111 of the cylinder 101 and/or a portion of the sidewall 103 near the proximal end cylinder cover 111 are also provided with a stop section 115 to restrict the first piston 102 from continuing to move toward the proximal end, thereby ensuring the minimum volume of the first inner chamber 121. In addition, since the first inner chamber 121 and the second inner chamber 131 are both chambers that contain fluid and bear certain fluid pressure, a number of seals are disposed at a contact portion of the first piston 102 or the second piston 103 with the surface of the cylinder 101. For example, as shown in FIG. 3, sealing rings are disposed at a contact surface of the first piston 102 or the second piston 103 with the cylinder 101. In some embodiments, gap sealing is adopted between the first piston 102 or the second piston 103 with the cylinder 101.

In some embodiments, the press-riveting device 100 further comprises a displacement sensor 106 to obtain the axial displacement of the first piston 102, thereby obtain the change in the axial position of the press-riveting end 123 thereon. As shown in FIG. 3, the sensor 106 is disposed on the proximal end cylinder cover 111, and the sensor body 161 thereof extends along the axial direction of the cylinder 101 toward the distal end, and partially extends into the first piston 102 and its press-riveting rod 122. Therefore, when the first piston 102 moves along the axis of the cylinder 101 toward the distal end, a relative movement occurs between the sensor body 161 and the first piston 102 and the press-riveting rod 122 thereof, and the length of the sensor body 161 extending into the first piston 102 changes, enabling the determination of the axial displacement of the first piston 102, and further determining of the change in the axial position of the press-riveting end 123. In some embodiments, the press-riveting device 100 may further include a pressure sensor (not shown in the figure), which is used to monitor the force state along the axial direction of the press-riveting rod 122, so as to obtain the output axial pressure of the riveting end 123. According to the detection of the displacement and output force of the press-riveting end 123 by the displacement sensor and the pressure sensor, the working state of the press-riveting device 100 can be known, and the quality of the press-riveting process can be monitored.

The portion shown in broken lines in FIG. 3 shows a possible assembling way of the cylinder of the press-riveting device 100, and the portion shown in broken lines schematically shows a frame, other parts or a corresponding position of a worktable of the press-riveting device 100. In some embodiments, the cylinder is installed at the frame, other parts or the corresponding position of the worktable of the press-riveting device 100 by means of connections such as welding, gluing, a threaded connection, or a snap connection at its distal part. In some embodiments, the cylinder can also be connected with the frame, other parts or the worktable of the press-riveting device 100 at other portions.

It can be seen that by using fluid pressure to drive the piston to move, the press-riveting device can have a more compact structure. In addition, the axial length of the press-riveting device can be shortened to suit a working environment with limited operating space.

FIGS. 4 to 6 show schematic diagrams of a press-riveting device 200 according to an embodiment of the present application; among them, FIG. 4 is a schematic view of the appearance of the press-riveting device 200; FIG. 5 is a side diagram of the press-riveting device 200; FIG. 6 is a cross-sectional view of the press-riveting device 200 along the AA direction shown in FIG. 5, wherein the press-riveting device 200 is in an initial state.

As shown in FIGS. 4 to 6, different from the press-riveting device 100 shown in FIGS. 1 to 3, the press-riveting device 200 is not provided with a spring element between the first piston 202 and the second piston 203. Instead of the spring element, an additional hydraulic system acts as a buffering force transmission element between the first piston 202 and the second piston 203. The first piston 202, the second piston 203 and the sidewall 213 define a third inner chamber 207. The third inner chamber 207 is in communication with the fluid pump system 205 through a third through hole 271 provided on the sidewall 213 of the cylinder 201 as shown in FIG. 4, so that it can input liquid to or extract liquid from the third inner chamber 207. Specifically, during the press-riveting operation of the press-riveting device 200 of this embodiment, when the sleeve section 232 abuts the workpiece to be press-riveted, it reaches the pre-compression position. Subsequently, the second piston 203 is forced to stop moving, while the first piston 202 continues to move toward the distal end along the axial direction of the cylinder 201. Since the third inner chamber 207 is filled with liquid at this time, with the movement of the first piston 202 approaching the second piston 203, the liquid is slowly pushed out or pumped out by the fluid pump system 205. In this process, due to the effect of the liquid pressure in the third inner chamber 207, the second piston 203 receives a pressing force, so that the workpiece to be press-riveted is better fixed, and the accuracy of the press-riveting position is ensured. Although not shown in the figures, in some embodiments, a pressure regulating valve 272 is provided between the third inner chamber 207 and the fluid pump system 205 to adjust the fluid pressure in the third inner chamber 207, so as to apply suitable pre-pressing force on the workpiece to be press-riveted.

Regarding other components of the press-riveting device 200 and their working methods, reference may be made to the corresponding description of the press-riveting device 100 shown in FIGS. 1 to 3, which will not be repeated here. It should be pointed out that in some embodiments, the buffering force transmission element between the first piston and the second piston of the press-riveting device also adopts an alternative structure and principle. For example, the two are respectively provided with repulsive magnetic elements, so that force is transmitted through the magnetic field.

It should be noted that although several modules or sub-modules of the press-riveting device are mentioned in the above-detailed description, this division is only exemplary and not mandatory. In fact, according to the embodiments of the present application, the features and functions of two or more modules described above may be embodied in one module. In contrast, the features and functions of one module described above may be further divided into multiple modules to be embodied.

Those skilled in the art may understand and implement other changes to the disclosed embodiments by reading the specification, the disclosed content, the drawings and the appended claims. In the claims, the wording “comprising” and “including” do not exclude other elements and steps, and the wording “a”, “an” and “one” do not exclude plurals. In the actual application of the present application, one component may perform the functions of multiple technical features recited in the claims. Any reference numerals in the claims shall not be construed as limiting the protection scope. 

What is claimed is:
 1. A fluid pressure operated press-riveting device, comprising: a cylinder having a distal end and a proximal end disposed opposite to each other, and a sidewall extending axially between the distal end and the proximal end, wherein the distal end has an opening section; a first piston, wherein the first piston is disposed in the cylinder and defines a first inner chamber together with the proximal end, and wherein the first piston has a press-riveting rod extending towards the distal end and aligned with the opening section; a second piston, wherein the second piston is disposed in the cylinder and defines a second inner chamber together with the distal end, the second piston has a sleeve section extending towards the distal end, the sleeve section extends at least to the opening section to close the opening section, and the sleeve section slidably accommodates the press-riveting rod; a fluid pump system, wherein the fluid pump system is in fluid communication with the first inner chamber and the second inner chamber, respectively, and is used to supply fluid thereto or suck fluid back therefrom, so that the first piston and the second piston can reciprocate axially along the cylinder, and wherein when the first piston and the second piston move from the proximal end to the distal end, the sleeve section moves to a pre-compression position, and then the press-riveting rod protrudes out of the sleeve section to perform a press-riveting operation on a workpiece to be press-riveted; and a force transmission member disposed between the first piston and the second piston, wherein when the sleeve section of the second piston reaches the pre-compression position, the first piston can approach the second piston and apply a pressing force to the second piston through the force transmission member.
 2. The fluid pressure operated press-riveting device of claim 1, wherein the force transmission member comprises a spring element with its two ends connected with the first piston and the second piston, respectively.
 3. The fluid pressure operated press-riveting device of claim 2, wherein the spring element is a Belleville spring element.
 4. The fluid pressure operated press-riveting device of claim 1, wherein the force transmission member comprises a third inner chamber defined jointly by the first piston, the second piston and the sidewall of the cylinder, and the fluid pump system is also in fluid communication with the third inner chamber to supply fluid thereto or suck fluid back therefrom.
 5. The fluid pressure operated press-riveting device of claim 4, wherein a pressure regulating valve is disposed between the third inner chamber and the fluid pump system to adjust a fluid pressure in the third inner chamber.
 6. The fluid pressure operated press-riveting device of claim 1, wherein a press-riveting end is disposed at an end of the press-riveting rod.
 7. The fluid pressure operated press-riveting device of claim 6, wherein the press-riveting end is detachably connected with the press-riveting rod.
 8. The fluid pressure operated press-riveting device of claim 6, wherein the sleeve section comprises a stop element to limit a length of the press-riveting end protruding from the sleeve section.
 9. The fluid pressure operated press-riveting device of claim 1, wherein a seal is disposed at a contact portion of the first piston or the second piston with a surface of the cylinder.
 10. The fluid pressure operated press-riveting device of claim 1, wherein the press-riveting device further comprises a displacement sensor connected with the first piston and configured to indicate an axial position of the first piston.
 11. The fluid pressure operated press-riveting device of claim 1, wherein the fluid pump system comprises a fluid pump, and the first inner chamber and the second inner chamber are in fluid communication with each other through the fluid pump.
 12. The fluid pressure operated press-riveting device of claim 1, wherein the fluid supplied and sucked by the fluid pump system is hydraulic oil. 